Truck not building air...leaking governor

Hello guys. I'm still confused why my 1993 Peterbilt 379 project truck isn't building air. Won't build over 20 pounds. The air governor under the hood was spewing air last time I started it so I replaced it but new one still spews air...so obviously that's part of the low air problem. I can't hear any leaks anywhere else even with the truck shut off. This truck has been setting for 5+ years. Already checked air dryer with truck running and purge valve seems fine.

NOTE: Something else to consider but may not be related to anything except low air pressure...when the brake pedal is pressed, it makes an air toot sound coming from behind the park brake knobs area on the dash.

 

Yes mounted to the compressor. Will try to get a pic sometime soon.

 

Yes I believe that's where the air is spewing from the governor. I put the lines back on the same way when I put on the new governor but it's STILL spewing. I reversed them just to make sure and didn't fix it so put them back.
Also, the latter part of your post, are you talking about hooking an air hose from a regular shop type air compressor into the trucks air tank coupler to build up the pressure? Or hooking direct to truck compressor?

 

Well I'll have to look again and the truck is on my farm 15 miles away. If I remember correctly, it's spewing out of the hole labeled EXH which I assume is exhaust

 

Ok I really appreciate you helping me narrow it down! I will give it another look in a few days. Thanks again for the info.